In manufacturing paper trays, a roll of paper is cut into many smaller pieces of paper which are called blanks. The blanks are then fed into a machine which uses shaped dies to stamp them into a desired shape and size.
The formed trays typically have a flange around the outer peripheral rim which provides structural rigidity and a mounting place for a lid. It is desirable to have a uniform flange on the tray not only to enhance its appearance, but also so that specific rigidity and mounting characteristics may be anticipated. In addition, a uniform flange enhances the ability of automated equipment to handle the tray with a minimum of difficulty.
Previously, a uniform flange was very difficult to attain. Because of the extreme deformations occurring to the paper, it was very difficult to predict the locations and amounts of deformations. Because of this problem, the manufacturers merely shaped the trays and then post-trimmed the flanges to a certain thickness, or discarded whichever trays did not meet their restrictions.
Recently the concern about the cost of materials and manufacturing has played an important part in deciding how to manufacture trays. By shaping and then trimming excess paper, a significant amount of waste is created. Additionally, because of the need to trim the tray, another manufacturing step is necessary.
Computer aided design machines have helped the manufacturing industry by allowing manufacturers to design a shape before making a working model of it and the dies used to shape it. With these computers, manufacturers can predict deformations and design a blank which, after being shaped, needs no trimming. This is contingent upon the correct alignment of the blank between the dies.
Upon researching the shape of the blank which would require no post trimming, it was discovered that the optimum blank would have rounded edges on nearly all sides. The disadvantage to having rounded edges is that it is very difficult to correctly align the blank by any conventional method.
Previously, the post-trimmed blanks were merely gravity fed onto a die and aligned with passive guide plates on each side of the die. The straight edged blank slid into position, was stamped into shape, and then trimmed in a subsequent operation.
The round edged blanks, however, tend to twist out of position when using the conventional passive guide plate arrangement. This stems from the fact that the round edged blanks do not contact the straight edged guide plates at enough points to be restrained from twisting. Because the blanks twist in the die, they have uneven flanges on their outer edges after stamping.
An additional disadvantage of having passive guides which have constant contact with the blank during sliding alignment is that usually the guides are hot due to transfer heat from the heated female die. This allows any plastic coating on the paper board to melt and stick to the heated guide plate as the blank attempts to slide into position. This sticking defeats the effect of gravity which is relied upon to align the paper board in the correct position.
Thus, the need arises for a device for positively positioning a round edged or otherwise oddly shaped paper blank on a die, requires no post trimming of the blank and does not allow enough contact to melt and stick to guides.